Although the Wizards never trailed at AmericanAirlines Arena, their victory was helped by an apparent no-call on a Bradley Beal travel which led to a three-pointer that put the Heat out of sight in the closing stages.
Miami dropped out of first place in the Eastern Conference and lost for the first time in team history while shooting at least 59% (59.4%).
After managing just 10 points in the third quarter, Brandon Knight scored 17 of his 21 points in the fourth and Mirza Teletovic rolled in a last-gasp basket to give the Suns their first win in five games.
Porzingis, who Nowitzki said is better than he was in his 20s, finished with a game-high 28, including 12 in the fourth, but the Mavs held on for a 104-97 success.
Kyle Lowry scored 27 to lead the way for the hosts, while Terrence Ross, in his first start of the season, put up 22 including a thunderous fourth-quarter dunk which sparked a Raptors run that ultimately sealed victory.
It was only LA's third away win of the season as DeAndre Jordan put up 20 points and 12 rebounds to inflict a fourth straight defeat on Minnesota.
Thomas scored 22 points on 9-13 shooting, including 4-4 from downtown, while Jared Sullinger tied a career-high with 20 rebounds for the Celtics.
Milwaukee trailed by four with 20 seconds to go, but then reeled off six points in a row to clinch victory, with Greg Monroe (16 points, 12 rebounds) making a late layup to seal it.
Results in full: Detroit Pistons 84-104 Charlotte Hornets, San Antonio Spurs 119-68 Philadelphia 76ers, Washington Wizards 114-103 Miami Heat, Dallas Mavericks 104-97 New York Knicks, Los Angeles Lakers 93-102 Toronto Raptors, Portland Trail Blazers 88-90 Milwaukee Bucks, Los Angeles Clippers 110-106 Minnesota Timberwolves, Boston Celtics 111-93 New Orleans Pelicans